Radiant energy is used in a variety of manufacturing processes to treat surfaces, films, and coatings applied to a wide range of materials. Specific processes include but are not limited to curing (i.e. fixing, polymerization), oxidation, purification, and disinfection. Processes using radiant energy to polymerize or effect a desired chemical change is rapid and often less expensive in comparison to a thermal treatment. The radiation can also be localized to control surface processes and allow preferential curing only where the radiation is applied. Curing can also be localized within the coating or thin film to interfacial regions or in the bulk of the coating or thin film. Control of the curing process is achieved through selection of the radiation source type, physical properties (for example, spectral characteristics), spatial and temporal variation of the radiation, and curing chemistry (for example, coating composition).
A variety of radiation sources are used for curing, fixing, polymerization, oxidation, purification, or disinfections due to a variety of applications. Examples of such sources include but are not limited to photon, electron or ion beam sources. Typical photon sources include but are not limited to arc lamps, incandescent lamps, electrodeless lamps and a variety of electronic (i.e., lasers) and solid-state sources.
An apparatus for irradiating a surface with ultraviolet light includes a lamp (e.g., a modular lamp, such as a microwave-powered lamp having a microwave-powered bulb (e.g., tubular bulb) with no electrodes or glass-to-metal seals), the lamp having reflectors to direct light (photons) on to the surface. The reflectors may desirably utilize a primary elliptical-shaped reflector. A typical reflector structure of a primary reflector is illustrated in FIG. 1.
In FIG. 1, a primary reflector 2 has a generally smooth elliptical shape. A bulb 4, typically electrodeless and containing a gas, is placed at the internal focus of the half-ellipse formed by the primary reflector 2. The bulb 4 and the reflector 2 extend linearly along an axis in a direction moving out of the page (not shown). The gas in the bulb 4 is excited to a plasma state by a source of radio frequency (RF) radiation, such as a magnetron (not shown). The atoms of the excited gas in the bulb 4 return to a lower energy state, thereby emitting ultraviolet light. The ultraviolet light rays 6 radiate from the bulb 4 in all directions, striking the inner surface 8 of the reflector 2 at various points along the reflector 2. The inner surface 8 of the reflector 2 is typically highly reflective, the reflector 2 being formed of or coated with a highly reflective material. The incoming rays 6 are reflected 10 toward the external second focus 12 of the half-ellipse reflector 2. A work product 14 to be cured is typically placed at the second focus 12. The bulb and reflector design are optimized to produce the maximum peak light intensity (lamp irradiance) at the surface of the work product (also propagating linearly out of the page). In circumstances where focusing the light to a fine point (line) is desirable, a very smooth surface with a high specular reflectance provides an ideal reflector design.
However, there are curing applications where high peak irradiance is not desirable, but a distributed total high energy over the surface of the work product is preferred. A reflector 2 of the design of FIG. 1 cannot provide such a solution. Light diffusers are known, such as described in U.S. Pat. No. 6,280,055 (the '055 patent). The '055 patent describes a light modifier, which is configured to function as an add-on reflector to uniformly illuminate a subject in photographic applications. Unfortunately, the reflector of the '055 patent does not spread a typically focused light pattern with high total energy.
Accordingly, what would be desirable, but has not yet been provided, is a reflector that produces a high total energy over a larger area of the surface of a work product while maintaining a high specular reflectance over the entire inner surface of the reflector.